One of the challenges of wireless communications is designing suitable antennas that can provide desired performance characteristics, yet are relatively small in size to fit within mobile devices. For example, with wireless devices such as mobile telephones, it is desirable to keep the overall size of the telephone as small as possible. Furthermore, internal antennas are generally preferred over external antennas, as externally mounted antennas take up more space and may be damaged while traveling, etc.
The use of an internal antenna in a handheld device, particularly those that can be held in various positions, such as by either, both or no hands, leads to the antenna environment being modified in different ways depending on how the user holds/positions the device. Accordingly, antenna designs have to be optimized for only a single position, e.g. one handheld scenario, or the antenna has to be designed to compromise between mulitple scenarios.
One example of an antenna that is implemented on a PCMCIA card to be inserted in a PCMCIA slot of a laptop computer is disclosed in U.S. Pat. No. 6,031,503 to Preiss, II et al. The antenna assembly includes two folded, U-shaped antennas, which may be dipoles or slot radiators, that are disposed orthogonally to one another to provide polarization diversity. Polarization diversity means that signals are transmitted and received on two different polarizations to increase the likelihood that the signal is received. Signals are carried to and from the antenna by microstrip feed lines. The microstrip lines are placed off center along each antenna slot to establish an acceptable impedance match for the antenna, and the feed lines are coupled to the communications card by coaxial cables.
Accordingly, with even more restrictive space constraints for such handheld devices, there is a need for antennas which are appropriately sized for such applications yet still provide desired performance characteristics.